Manufacture of electron discharge devices



Aprll 28, 1964 J. P. FIORE 3,130,474

MANUFACTURE OF ELECTRON DISCHARGE DEVICES Filed July 50, 1962 llIIIIIII/IIIIIII. I 'IIIIIIIIIIIIIIIIA INV NTOR. 30 JosephPP z ore United States YPatent Ofifice 3,139,474 Patented Apr. 28, 1964 3,130,474 MANUFACTURE OF ELEi'JTRflN DESCHARGE DEVICES Joseph P. Fiore, Chicago, 121., assignor to The Rauland Corporation, Chicago, iii, a corporation of lilinois Filed July 34), 1962, Ser. No. 213,514

' 3 Claims. (Cl. 2925.17)

The present invention is directed to a method of manufacturing an electron gun for a cathode-ray tube and concerns itself most particularly with process steps by means of which it is possible to achieve a precisely controlled axial separation of the first and second grid electrodes characteristically included in such an electron gun.

It is known that the separation of these electrodes has a distinct bearing, for example, on such properties of the tube as cut-ofi potential, spot size and shape and for this reason manufacturing techniques adopted in thepast have looked to precisely controlled axial separation of the grids in question.

Of course, accurate control of grid spacing is highly desirable for monochrome tubes in order to attain the desired operating characteristics of the tube and also to have uniformity of product. These same considerations apply to multi-gun cathode-ray tubes such as those employed in color television receivers. But here the prob lem becomes even more acute because of the requirement that the several electron guns exhibit closely controlled relatively operating characteristics. While manufacturing processes have been developed which permit the manufacture of electron guns for monochrome tubes with totally acceptable characteristics, even if made in mass production, it has been found that they are not sufficiently precise for the more stringent requirements of multi-gun cathoderay tubes.

In accordance with one prior process, the several electrodes of the gun are first individually formed and centrally apertured after which they are assembled onto a mandrel or other positioning structure with the electrode apertures in coaxial alignment. The axial spacing of the several electrodes, particularly that of the first and second grids, is usually established by the insertion of suitable gauges between adjacent electrodes within the assembly. The assembly is then compressed and the electrodes are secured against relative movement by aifixing mounting projections which extend from the electrodes into insulating posts or rods in parallel relation to the gun axis. Having thus secured the electrodes in the gun assembly, the gauges are removed and the gun is now ready for further processing in accordance with known techniques.

The first and second grids are flat planar structures and the separating gauge is likewise a planar structure of critically controlled thickness. When the electron gun is fabricated as described, there is a very large area of contact between the gauge and the contiguous faces of the first and second grids and withdrawal of the gauge tends to disturb the relative orientation of the electrodes and even to establish tensions within the electrodes which frequently result in misalignment of the electrodes and impairment of the gun properties. The short-comings of such fabricating techniques are most pronounced in the manufacture of electron guns for multiple gun cathode-ray tubes.

It is therefore a principal object of the invention to provide a new and improved method for the manufacture of an electron gun for a cathode-ray tube having contiguous, coaxially aligned and apertured first and second grids with a critically controlled axial separation.

It is another object of the invention to provide a method for the manufacture of such an electron gun which lends itself to the fabrication of monochrome as well as color cathode-ray tubes.

It is another and specific object of the invention to provide a method for the manufacture of an electron gun which avoids the aforementioned limitation of prior processes.

The invention concerns the manufacture of an electron gun for a cathode-ray tube having contiguous, coaxially aligned and apertured first and second grid electrodes characterized by precisely controlled axial separation of the grid apertures. The steps of the invention comprise forming a pair of similar and apertured electrodes of generally planar construction and forming on one face of each such electrode, near the periphery thereof, at least one projection having a surface area that is a minor fraction of the surface area of the electrodes and having a depth, measured with respect to the portion of the electrode immediately surrounding its aperture, which corresponds to a preaetermined fractional portion of the desired grid aperture axial separation. The method further contemplates positioning the electrodes with their apertures in coaxial alignment, with their projections in facing alignment and with a gauge between and in contact with the facing projections to establish the separation of the grid apertures at the desired predetermined amount. Thereafter, the electrodes are secured against relative movement and tire gauge is removed from between the electrode projections,

The features of the present invention, which are believed to be novel are set forth with particularity in the appended claims. The organization and manner of operation of the invention, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is a schematic cross-sectional view of a cathode'ray image reproducer having an electron gun constructed in accordance with the method of the invention;

FiGURE 2 is an enlarged cross-sectional view of the electron gun showing one step in the assembly of two of its electrodes; and

FIGURE 3 is an enlarged cross-sectional view illustrating another method step of the invention.

While an electron gun constructed in accordance with the invention is applicable to a single gun monochrome picture tube or to a multiple-gun color picture tube, the drawing and explanation are simplified by considering the single gun monochrome case and, for convenience, it will be assumed that the tube structure of FIGURE 1 is such a device. Moreover, since the invention concerns the gun as distinguished from the other components of the cathode-ray tube, such other components have been in dicated but have not been drawn in complete detail, again for purposes of simplification.

Referring now more particularly to FIGURE 1, the cathode-ray tube there represented comprises an envelope It having a neck portion 11 of relatively small diameter which accommodates the usual tube base 12 at one end and merges with the familiar conical section 13 at its opposite end. Conical section 13 terminates in a faceplate or screen 15 which bears a coating 16 of luminescent material on its inner surface and this coating is backed by the customary thin film 17 of aluminum or other conductive material. Conical section 13 accommodates a high voltage connection (not shown) which is popularly referred to as the high voltage button through which final anode or ultor potential is applied to the tube. A coating of conductive material, such as graphite, on the inner surface of cone 13 extends the high voltage connection to aluminum layer 17 and also extends into the leading portion of neck 11 to facilitate the application of high voltage potential to the uni-potential lens of the electron gun of the tube which is housed within the neck.

The elements of the electron gun are conventional and include a cathode cylinder Zl which is opened at one end to receive the usual heater structure (not shown) and bears at its opposite end a coating of electron emissive material. Positioned in front of cathode 21, in the direction of screen 15 and in the order named, are a first grid 22 and a second grid 23. It is customary that these grids take the form of cylinders open at one end and closed at the other end with the closure portion centrally apertured and serving as a generally planar electrode disposed transversely of the gun axis. The grid cylinders are positioned with their closed ends adjacent but separated by a critically controlled amount in a manner to be described more particularly hereinafter. An insulating disk permits cathode 21 to be supported within grid cylinder 22 with a controlled separation of its emitting surface from the grid aperture.

Following the first and second grids is a uni-potential lens system comprising anodes 2- and 25 and a focus electrode 25. Anodes 24 and 25 are conductively connected and thus maintained at the same operating potential and their facing end portions project within focus electrode 26 from which this structure derives the name immersion lens by which it is frequently known. Resilient contact elements 27 projecting from anode 25 contact the conductive coating of conical section 13 to extend the high voltage connection of the tube to anodes 24, 25. Additional spring elements 28 project from the forward portion of the gun structure to engage envelope section 11 for the purpose of centering the gun within the neck of the tube. The electrodes of the gun assembly are in coaxial alignment With the tube axis AA and are maintained in a desired relative position by means of mounting elements 259 extending from the electrode elements and anchored to insulating posts :13 and 19. Certain of the electrodes are provided with individual electrode leads which connect with pins (not shown) of the tube base 12 in customary fashion.

As thus far described, the tube structure is completely conventional and will be recognized as the structure generally employed as the image reproducer of television receivers. Since this is such a well known device, it is believed that a description of its operation is unnecessary and attention may now be directed to the method of the invention for the manufacture of the electron gun, especially to attain a precisely controlled axial separation of the apertures in grids 22 and 23. For this purpose, reference is made to FIGURE 2.

In the manufacture of an electron gun in accordance with the invention the first and second grid electrodes of generally planar construction are first formed; as explained above, these electrodes are the end closure members 26 and 27 of a pair of conductive cylinders 22, 23 open at one end but closed .at the other. Each closure member of these cylinders, serving as an electrode, is centrally apertured as designated by reference characters 22a and 23a.

Further in accordance with the invention there is formed on one face of each of these electrodes, near the outer periphery thereof, at least one projection having a surface area that is a minor fraction of the surface area of the electrode and having a depth, measured with respect to the portion of the electrode immediately surrounding its aperture, which corresponds to a predetermined fractional portion of the desired inter-electrode separation. While such projections may be formed in various Ways on the electrode surface, it is particularly convenient since the electrode is the closure portion of a cylindrical structure to form the projection as an annular bead constituting the connection of the planar electrode surface with the cylindrical section for which it is a closure. Accordingly, cylindrical structure 22 is formed with an annular bead 24 while cylindrical structure 23 has a similar annular head 25.

Having thus formed the apertured electrodes with their respective peripheral projections, they are positioned in the manner shown in FIGURE 2 with their apertures in coaxial alignment and with projections 2-4, '25 facing one another. A gauge 23 is inserted between and in contact with facing projections 24 and 25 and the separation of grid apertures 22a, 23a is determined by the thickness of the gauge and the set-back of planar surfaces 26, 27 of the electrodes with respect to their projections 24, 25. By appropriate dimensioning the desired axial spacing of the grid apertures is readily obtained. From this point forward the gun is assembled in accordance with the aforedescribed previous practice, namely, the other electrode elements are established in axial alignment with grid cylinders 22, 23, a compression is applied to the assembly to establish and maintain the assembly; and, finally, the electrode projections 29' are secured to insulating mounting posts 13, 19. Thereafter, gauge 28 is withdrawn.

It will be observed that the contact area of the gauge with the contiguous surfaces of cylindrical structures 22, 23, is very smml indeed in comparison with the practices of the prior art. It has been found that the gauge may be withdrawn without adversely affecting either the alignment of the electrode elements of the configuration of the grid apertures due to stresses and tensions attributable to movement of the spacer gauge.

A modification of the method of the invention involves the step represented in FIGURE 3 where grid cylinders 22, 23 have closure members 39, 31 respectively centrally apertured to serve as the first and second grid electrodes but instead of being strictly planar in the formal sense of that term, they are dished to be symmetrically concave in cross-section as shown. In this case the outer peripheral portions of the electrodes which correspond to the meeting plane of the electrodes and the cylinders of their structures serve the same purpose as annular projections 24, 25 of the embodiment of FIGURE 2.

In both PHGURES 2 and 3 gauge 23 is shown to have a centrally located aperture 32 which is used in establishing the desired couial alignment of the parts in the initial assembly stages of the gun.

The described process of assembling an electron gun is most simple to practice and permits precise axial spacing of the apertures of the first and second grid electrodes. At the same time, it has been found to avoid shortcomings of the prior art process and is eminently suited for mass production.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In the manufacture of an electron gun for a cathode ray tube having contiguous and coaxially aligned apertured first and second grid electrodes with the axial separation of their apertures controlled to a predetermined amount, the steps of: forming a pair of similar and apertured electrodes of generally planar construction; forming on one face of each of said electrodes near the periphery thereof at least one projection having a surface area that is a minor fraction of the surface area of said electrode and having a depth, measured with respect to the portion of said electrode immediately surrounding the aperture thereof, corresponding to a predetermined fractional portion of said axial separation; positioning said electrodes with said apertures in coaxlal alignment, with said projections thereof in facing alignment and with a gauge element between and in conct With said facing projections to establish the separation of said apertures at said predetermined amount; face of each of said electrodes is formed by dishing each securing said electrodes against relative movement; and such electrode to be symmetrically concave in crossrernoving said gauge element from between said projecsection. tions.

2. The method of manufacturing an electron gun in 5 References Cited in the file of this patent accordance with claim 1 in which the projection on one face of each of said electrodes is formed as an annular UNITE D STAT-BS PATENTS head at the outer periphery of each such electrode. 2,189,986 Hickok Feb. 13, 19 0 3. The method of manufacturing an electron gun in 2,415,412 Buchwald Feb. 11, 1947 accordance with claim 1 in which the projection on on 10 2,544,934 Nase Mar. 13, 1951 

1. IN THE MANUFACTURE OF AN ELECTRON GUN FOR A CATHODE RAY TUBE HAVING CONTIGUOUS AND COAXIALLY ALIGNED APERTURED FIRST AND SECOND GRID ELECTRODES WITH THE AXIAL SEPARATION OF THEIR APERTURES CONTROLLED TO A PREDETERMINED AMOUNT, THE STEPS OF: FORMING A PAIR OF SIMILAR AND APERTURED ELECTRODES OF GENERALLY PLANAR CONSTRUCTION; FORMING ON ONE FACE OF EACH OF SAID ELECTRODES NEAR THE PERIPHERY THEREOF AT LEAST ONE PROJECTION HAVING A SURFACE AREA THAT IS A MINOR FRACTION OF THE SURFACE AREA OF SAID ELECTRODE AND HAVING A DEPTH, MEASURED WITH RESPECT TO THE PORTION OF SAID ELECTRODE IMMEDIATELY SURROUNDING THE APERTURE THEREOF, CORRESPONDING TO A PREDETERMINED FRACTIONAL PORTION OF SAID AXIAL SEPARATION; POSITIONING SAID ELECTRODES WITH SAID APERTURES IN COAXIAL ALIGNMENT, WITH SAID PROJECTIONS THEREOF IN FACING ALIGN- 